1. Field of the Invention
The present invention relates of a reaction curable resin composition and an artificial marble obtained by molding and curing the composition. More particularly, the present invention relates to a reaction curable resin composition for the production of an artificial marble having high mechanical strength and excellent weather resistance and stain resistance and having an excellent processability, and an artificial marble obtained by molding and curing such a composition.
2. Discussion of Background
Heretofore, an artificial marble prepared by molding and curing a resin composition is practically employed for various applications including sanitary wares such as toilet tables, bath tabs or kitchen counters, and building interior or exterior materials. To obtain such an artificial marble in the form of a molded resin product, it is common to employ a casting method wherein a composition prepared by blending and mixing e.g. inorganic fillers or fibrous reinforcing material to a resin as matrix constituting the artificial marble is filled in a mold, followed by curing. Otherwise, a compression molding method is employed by using SMC (sheet-molding compound) which is prepared by blending inorganic fillers, a thickener and other additives to a resin, impregnating the blend to e.g. glass fibers and enclosing the impregnated glass fibers with a film to form a sheet, or BMC (bulk-molding compound) which is prepared in the same manner but in a bulk form.
The matrix resin used in such molding methods, is usually an unsaturated polyester resin. However, an artificial marble made of such a resin is more or less inferior in its appearance. For example, an artificial marble prepared by using an unsaturated polyester resin as matrix, has little transparency and thus has a drawback that an appearance due to transparency specific to marble can not be obtained. It has been proposed to overcome such a drawback (Japanese Unexamined Patent Publications No. 66462/1984 and No. 101552/1986).
On the other hand, reflecting an increasing demand for high quality, the artificial marble is required to have an appearance which gives a gorgeous impression with the internal patterns of the molded product to be seen through due to the transparency, to have mechanical strength such as flexural strength and impact strength and to have improved surface hardness or the heat resistant properties. Accordingly, an attention has been drawn to a methacrylate resin having good transparency and mechanical strength as such a matrix resin.
A number of proposals have been made with respect to an artificial marble or a composition for an artificial marble wherein a methacrylate resin is used as matrix. As basic proposals, a product obtained by curing a mixture of a methyl methacrylate polymer with an alumina hydrate (Japanese Examined Patent publication No. 22586/1975, U.S. Pat. No. 3,847,865) and a granite product composed of opaque or translucent particles of predetermined particle sizes wherein a methyl methacrylate polymer and alumina trihydrate particles are used as matrix (Japanese Unexamined Patent Publication No. 72707/1977 and U.S. Pat. No. 4,085,246), are known. Further, as proposals having a feature in the combination with a filler, it has been proposed, for example, to incorporate aluminum hydroxide (Japanese Examined Patent Publications No. 22586/1975 and No. 43222/1980), to incorporate a combination of aluminum hydroxide with either one of magnesium hydroxide, magnesium carbonate and aluminum oxide (Japanese Unexamined Patent Publication No. 104621/1978), to incorporate silica (Japanese Unexamined Patent Publication No. 4611/1981), and to incorporate calcium silicate (Japanese Unexamined Patent Publication No. 33308/1984). Further, a methacrylate resin composition containing a filler and having its fluidity during the molding improved, is also disclosed (Japanese Unexamined Patent Publication No. 245609/1985).
As described in the foregoing, the matrix resin is being changed from an unsaturated polyester resin to a methacrylate resin.
Further, an artificial stone molded product has also been proposed which is composed of a polymer of a composition comprising as matrix a polyfunctional allylcarbonate resin, preferably diethylene glycol bis(allylcarbonate) polymer, known as a resin having excellent transparency as well as high strength and abrasion resistance and fine powder of silica or alumina hydrate (Japanese Unexamined Patent Publication No. 111953/1986).
As described in the foregoing, the matrix resin for an artificial marble is desired to be a resin having excellent transparency so that the molded artificial marble will have an appearance which gives a gorgeous impression, and for this purpose, a methacrylate resin is generally regarded as a suitable resin. However, there is a problem that the methacrylate resin and filler are usually substantially different in various properties, and the resin and the filler have poor affinity or adhesion particularly due to the difference in their interfacial properties. Further, when the filler is incorporated, the viscosity increases by the incorporation, whereby it becomes extremely difficult to uniformly disperse the filler. Accordingly, there is a problem that it is difficult to improve the properties of the artificial marble or to reduce the cost by increasing the amount of the filler.
Consequently, the artificial marble thereby obtained has a drawback that the mechanical strength such as the flexural strength or impact strength is pratically inadequate. In order to overcome such drawback, it has been proposed that the filler is subjected to surface treatment, for example, with a silane coupling agent, and such a surface-treated filler is incorporated to a resin. However, no adequate effect has yet been obtained. Besides, an increase of the manufacturing cost is thereby unavoidable. Furthermore, no adequate stain resistance or chemical resistance will be obtained by such a means for improvement.
Similar problems exist in the case where a polyfunctional allylcarbonate having excellent transparency is used as the matrix resin. Namely, diethylene glycol bis(allylcarbonate) has poor affinity and adhesion to an inorganic filler. Accordingly, the inorganic filler is not adequately dispersed in the matrix resin, whereby it is extremely difficult to incorporate a substantial amount of the filler. Even when the filler is incorporated in a small amount, it is likely that the filler is non-uniformly present in the molded product as an artificial marble, whereby a gorgeous appearance is hardly obtainable. Besides, the mechanical strength tends to be low. For example, when being cut or drilled for processing, the molded product is likely to undergo breakage to form a defective product.
With a composition containing diethylene glycol bis(allylcarbonate) as the matrix resin, it is necessary to heat it to gradually raise the temperature to obtain a molded product, whereby an extremely long time is required.